An interview is usually just for *you* to get to know the college through talking to an alum. You are correct in that it is not evaluative; it will have no bearing on your ultimate decision. That said, I'm sure a egregiously bad interview may hurt your chances and an outstanding one may warrant a nice write up by your interviewer to the admissions office. Just accept the interview and don't sweat it. It doesn't mean much in terms of your ultimate decision, but it can never be a bad thing.